Murine monoclonal antibodies and human alloantisera specific for HLA inhibit monocyte phagocytosis of anti‐D‐sensitized human red blood cells

Abstract

Evidence is presented that monoclonal antibodies (mAb) against some human major histocompatibility complex (MHC) gene products and human sera containing HLA antibodies strongly inhibit immune phagocytosis of anti-D-sensitized red blood cells by human monocytes. w6.32HL, a mAb against a monomorphic class I antigen of high cell surface density, revealed the strongest inhibition among mAb reactive with MHC class I products. mAb with preferential reactivity for monomorphic and polymorphic DR and DQ epitopes (L203, L227, IIIE3, Tü22, Genox 3.53 and IV12) were noninhibitory. Definite inhibition was also apparent with a mAb against DRw52/MT2 (I-LR2) and with an antibody to class II antigens of high cell surface density (2MC3). Human sera containing HLA antibodies showed strong inhibition of immune phagocytosis up to a dilution of 1/1000. This inhibition could not be abrogated by platelet absorption. This indicates that human sera inhibiting immune phagocytosis may comprise at least two types of antibodies: cytotoxic HLA-specific antibodies which may or may not be inhibitory, and inhibitory antibodies against monocytic antigens not necessarily cytotoxic. These latter antibodies may recognize HLA DR or another as yet undefined gene product within, or closely associated to, the human MHC.

Reduced Immune Phagocytosis of Monocytes from Neonates Whose Mothers Produce HLA Antibodies

“…In addition, the cytotoxicity test on adher ent monocytes [7] and the IPI test [2] were carried out employing a cell panel of selected donors ( Higher sensitization, e.g. using undiluted anti-D, results in higher IP: x±SD=59±7% [1]. Low sensitiza tion, however, especially is apt to demonstrate an overall decrease of IP on monocytes from neonates compared to the IP in adults, and especially low IP in monocytes from those neonates whose mothers have produced HLA anti bodies (table II).…”

“…The analysis of immune phagocytosis was carried out by a mod ification of the IPI test [1,2] omitting the inhibitory HLA antibody in vitro, and assuming its effect in vivo. In this way a 'direct IPI test' in analogy to the direct antiglobulin test was performed.…”

“…We have developed a test procedure, the IPI test [1,2], which is positive in virtually all pregnancy sera which contain cytotoxic HLA ABC and DR antibodies [3]. In addition to these sera which are about 20-25% of all pregnancy sera, the IPI test detects those HLA antibodies which are not or only insufficiently cytotoxic.…”

“…IP inhibi tion (IPI) lasts for several days. The uptake of bacteria, fungi or foreign particles which does not depend on the Fc receptor is not inhibited [1][2][3].…”

NA1/NA2 Antisera Inhibit FcγRI- but Not FcγRII- Mediated Phagocytosis

“…The mechanism of this effect may be explained by the formation of three-molecule complexes in which the NA antibody binds via its Fab region to the respective antigen on the FcγRIIIb and with its Fc region, to the Fc binding site on the FcγRI. This phenomenon, which was first described by Kurlander [13]for HLA antibodies, has also been observed by us for HLA antibody binding to monocytes [14]and for monoclonal antibodies specific for FcγRII and FcγRIII binding to PMN [6]. After inducing the expression of lysosomal enzymes like proteinase 3 or myeloperoxidase on the PMN surface, binding of mAbs with specificity for these proteins led to the generation of oxygen radicals by the same mechanism [7, 8].…”